This invention relates to power amplifiers for electrical signals and more particularly to a signal modulated power amplifier having high efficiency of operation over a wide range of operating conditions.
RF amplifiers whose DC potential voltages are continuously varied to match signal level requirements for maintaining high efficiency operation throughout a predetermined range of input signal levels are generally known. One such example is disclosed in U.S. Pat. No. 3,413,570 entitled, "High Efficiency RF Power Amplification With Modulation Signal Controlled On-Off Switch Varied Amplifier DC Potentials", issued to W. B. Bruene, et al. on Nov. 26, 1968. There both non-linear and linear amplifiers are operated at a relatively high efficiency by modulation of the RF amplifier DC supply potentials which are caused to vary continuously in accordance with the amplitude of the modulating input signal.
Another such example is disclosed in U.S. Pat. No. 4,320,350 entitled, "Sliding Power Supply For RF Power Amplifier", by Michael J. Drapac. In that invention the power supplied by a sliding power supply to a power amplifier is indirectly controlled by a single feedback loop which operates in accordance with the load impedance voltage standing wave ratio of the amplifier.
Accordingly, it is an object of the present invention to provide improved control of an RF amplifier for maintaining power amplifier efficiency at a relatively high level.
It is another object of the present invention to provide an improvement in power supply and signal modulation of an RF amplifier for providing improvement in efficiency over a wide range of load, line voltage and envelope power.
Still a further object of the present invention is to provide a two loop feedback control of an RF amplifier for providing an improvement in amplifier efficiency.